Many cancer patients are exposed to both radiation and cytotoxic agents, and therefore, an evaluation of carcinogenic potential of medical treatment with drugs is a logical extension to the Branch's study of radiation-induced second cancers. Other non-therapeutic drugs are also studied when of special interest. Studies of multiple primary cancers are conducted to generate hypotheses about host and environmental determinants of specific cancers. Cancer patients under study include those reported to population-based cancer registries (especially the SEER program), persons treated at major institutions, and those treated in randomized clinical trials. Additional details on collaborative projects can be found in Project No. Z01CP04410-GEB, "Studies of Persons at High Risk of Cancer" and Project No. Z01CP04417-GEB, "Carcinogenic Effects of Therapeutic Drugs." A study of leukemia after non-Hodgkin's lymphoma found significantly increased risks following therapy with prednimustine, mechlorethamine and procarbazine, and high dose therapy with chlorambucil. In contrast, low risks were associated with the cyclophosphamide regimens in most common use in the United States. Radiotherapy was linked to a significantly increased twofold risk of non-lymphocytic leukemia among patients with uterine corpus cancer. Age at exposure did not influence susceptibility to radiation-induced leukemia. Second cancer incidence was found to be much higher among retinoblastoma patients with bilateral disease who are genetically predisposed to neoplasms compared to those with unilateral disease. Long-term survivors of cervical cancer experienced a twofold risk of cancer in moderately or heavily irradiated organs, particularly cancers of the rectum, vagina, vulva, ovary, and bladder. Young single men with Kaposi sarcoma, most of whom are presumed to be AIDS related, had a 200-fold risk of non-Hodgkin's lymphoma, but only a marginal increase of all other tumors.